1. Field of the Invention
The present disclosure relates to rotary blades, and more particularly to track and balance performance adjustments for rotary blades.
2. Description of Related Art
Aircraft manufacturers and maintainers commonly manage aircraft vibration to limit its effects on crew fatigue and expected service life of aircraft components. A significant contributor to vibration on certain types of aircraft, such as rotary wing aircraft, is rotary blade track and balance. Blade track relates to the tendency of a given blade to depart from the path or paths taken by predecessor blades in an aircraft blade set. Blade balance relates to the relative weight of each blade at the hub in relation to the others. Since track and balance performance can change due to various factors, such as manufacturing variation between blades within a blade, water absorption, or erosion during the blade service life, rotary blade track and balance is typically monitored and, if necessary, adjusted to improve aircraft vibration levels. Blades generally include one or more adjustment mechanisms that influence blade track and balance performance, such as provisioning for increasing or reducing hub weights, changing pitch rod length, and/or trim tabs for altering blade contour during rotation.
Change to one adjustment mechanism can influence other adjustment mechanisms of the blade or other blades in the blade set. For example, a hub weight change to one blade can alter the track of that blade, thereby creating the need for an offsetting trim tab adjustment. Since adjustments can be resource intensive, conventional track and balance adjustment algorithms typically model a group of alternative track and balance adjustment solutions for a given rotary blade set in order to select one most appropriate given the condition of the blade set and adjustment interactions.
One challenge to determining an appropriate track and balance adjustment solution for a rotary blade set is the size potential of the adjustment solution set. For example, in an aircraft with 16 adjustment-on/adjustment-off variables, e.g. four blades with four adjustment mechanisms per blade, there are 216 or 65,536 alternative adjustment-on/adjustment-off variable combinations. Each combination in turn can have multiple adjustment solutions with different adjustment values. Since each alternative adjustment solution can have a different expected performance, exhaustive search of the solution space by determining expected performance for each solution is normally not done. Instead, conventional adjustment algorithms only explore a subspace of the solution space typically by not optimizing candidate adjustment solutions for higher harmonics (e.g. those with frequencies above 2 times per rotation) and/or restricting exploration of the solution space.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is a need in the art for improved systems and methods for determining track and balance adjustment solutions. The present disclosure provides a solution for these problems.